Final Report Revision: Contract #53-91s8-5-eco54 Acute Effects of Canopy Reduction on California Spotted Owls: Challenges for Adaptive Management

INTRODUCTION The effect of logging on spotted owls (Strix occidentalis) and their habitat has been one of the most pressing wildlife conservation questions facing western forest managers for the past 30 years. Two subspecies, the northern and Mexican spotted owls (S. o. caurina and S. o. lucida, respectively), have been listed as threatened, in part, based on the loss of habitat due to logging (Gutiérrez et al. 1995). Although not currently listed, the third subspecies, the California spotted owl (S. o. occidentalis), has been proposed for listing, again partly based on past losses of habitat and the potential for future habitat loss as a result of existing U. S. Forest Service (USFS) management guidelines (USFWS 2003, 2005, 2006). Despite these events and the concern over the effect of logging on the spotted owl, there has not been a single controlled experiment to evaluate these effects. This is noteworthy because the need for controlled experiments on spotted owl responses to logging has been recognized by biologists since 1984 (Gutiérrez 1985). Executing a controlled experiment to examine the response of spotted owls to various approaches to forest management is problematic for two primary reasons, logistical challenges (e.g. timing of treatments, variability of logging crews, etc.) and the great variety of events that can occur under the rubric of “logging” on national forests. Logistical challenges arise because the scale of experiments must be very large to encompass natural variation in owl home range size, habitat composition and habitat selection behavior by owls, as well as ensuring that treatments are sufficiently large to enhance the possibility of a detecting a treatment effect should one occur. With respect to the second difficulty, the types of logging that could be evaluated require substantially different designs and considerations, not the least of which is the potential for a treatment to displace an owl pair from an established territory (in two of the spotted owl subspecies this would be considered a “taking” under the U. S. Endangered Species Act). The impact of logistical challenges cannot be overstated because logging of public land requires a great deal of legal and professional preparation, including the bidding of contracts with specific constraints or conditions that are not usually encountered by logging contractors. Contract constraints or conditions may create uncertainty for logging contract bidders or even result in few or no bids, which could affect the sale of trees within territories. Consequently, researchers would lose direct control over the timing of logging treatments, and hence timing of treatments among treatment subjects (owls). Logistics also involve oversight and potential legal challenges by stakeholders who are concerned about the activity, which could affect timing of logging treatments differentially or eliminate them completely. Thus, it is not surprising that there have been no large designed experiments assessing the influence of logging on owls, despite the great interest in these affects.